The rubbing process in the coupling and alignment process of the liquid crystal panel is also known as rubbing orientation. Typically materials such as nylon, fibers or cotton are used to rub the orientation films on the surfaces of the array substrate and the color filter substrate so as to change the surface state of the orientation films, thereby the liquid crystal molecules can be arranged uniformly with certain pre-tilt angle between the array substrate and the color filter substrate. The orientation quality has a significant impact on the basic properties of the liquid crystal display such as display uniformity, viewing angle, color difference, response speed, threshold voltage and the like.
The traditional process for forming an orientation film includes placing the array substrate or the color filter substrate to be oriented on a rubbing base, wrapping a rubbing cloth around a rubbing roller, rotating the rubbing roller to rub the rubbing cloth on the surface of the orientation film so as to form the orientation grooves (i.e. change the surface state of the orientation film). The orientation quality is closely related to the shape accuracy, flatness of the rubbing base, the gap accuracy between the rubbing base and the rubbing roller, and so on. The gap accuracy between the rubbing base and the rubbing roller will most affect the pushing amount, torque and other parameters of the rubbing process. Therefore, the gap accuracy between the rubbing base and the rubbing roller is mostly important to the rubbing process, and shall be controlled and measured precisely.
Existing tools for measuring the gap accuracy between the rubbing base and the rubbing roller have components as shown in FIG. 1, include a plug sheet 101 and a plug gauge 103. The plug sheet 101 is a plastic article containing an empty box 102, the length and width of the empty box 102 are the same as that of the plug gauge 103 so that the empty box 102 is just enough to contain the plug guage gauge 103. The thickness and the number of the plug guage 103 can be set according to the specifications of the gap accuracy. Currently, the industry specification of the gap accuracy is usually 3±0.035 mm, therefore the thickness of the plug guage 103 is typically 2.965 mm, 2.975 mm, 2.985 mm, 2.995 mm, 3.005 mm, 3.015 mm, 3.025 mm, 3.035 mm, and also may be 2.96 mm, 2.97 mm, etc. Existing plug guage 103 is a metal article, and its thickness is at least larger than that of the plug sheet 101.
Existing method for measuring the gap is shown in FIG. 2, wherein the plug guage 103 is placed into the empty box 102, then the plug sheet 101 is moved manually to the gap between the rubbing base 5 and the rubbing roller 6, and the size of the gap is measured roughly by using the thickness of the plug guage 103. FIG. 2 shows three cases where, from right to left, the thickness of the plug guage 103 is larger than the gap, the plug guage 103 is just passing through the gap and the thickness of the plug guage 103 is smaller than the gap. Such measurement method is inefficient, the plug guage 103 shall be successively replaced to measure the size of the gap. In existing production line, for example, in order to reflect the gap accuracy between the rubbing base 5 and the rubbing roller 6, the gap values at about 500 positions should be measured. If the plug guage 103 needs to be successively replaced during measurement, it will take too much time and seriously affect the utilization rate of the equipment.